Silicon

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	Silicon

Notable Characteristics

In its crystalline form, silicon has a metallic luster and a grayish color. Even though it is a relatively inert element, silicon still reacts with halogens and dilute alkalis, but most acids, (except for hydrofluoric acid[?]) do not affect it. Elemental silicon transmits more than 95% of all wavelengths of infrared light.

Applications

Silicon is a very useful element that is vital to many human industries. Silicon dioxide in the form of sand and clay is an important ingredient of concrete and brick and is also used to produce Portland cement. Silicon is a very important element for plant and animal life. Diatoms extract silica from water to build their protective cell walls. Other uses:

It is a refractory material used in high-temperature material production and its silicates are used in making enamels[?] and pottery.
Silicon is an important constituent of some steels.
Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and is used to make window glass, containers, and insulators, among many other uses.
Silicon carbide is one of the most important abrasives[?].
Ultrapure silicon can be doped with arsenic, boron, gallium, or phosphorus to make silicon more conductive for use in transistors, solar cells and other semiconductor devices which are used in electronics and other high-tech applications.
Silicon can be used in lasers to produce coherent light with a wavelength of 4560 angstroms.
Silicones are flexible compounds containing silicon-oxygen and silicon-carbon bonds; they are widely used in applications such as artificial breast implants and contact lenses.
Hydrogenated amorphous silicon has shown promise in the production of low-cost, large-area electronics and solar cells.

History

Silicon (Latin silex, silicis meaning flint) was first identified by Antoine Lavoisier in 1787, and was later mistaken by Humphry Davy in 1800 for a compound. In 1811 Gay Lussac and Thenard[?] probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. In 1824 Berzelius prepared amorphous silicon using approximately the same method of Lussac. Berzelius also purified the product by repeatedly washing it.

Occurrence

Silicon is a principal component of aerolites[?] which are a class of meteoroids and also of tektites[?] which is a natural form of glass.

Measured by weight, silicon makes up 25.7% of the earth's crust and after oxygen is also the second most abundant element. Elemental silicon isn't found in nature. It occurrs most often as oxides and as silicates. Sand, amethyst, agate, quartz, rock crystal, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.

Silicon is commercially prepared by the heating of silica and carbon in an electric furnace by using carbon electrodes. The Czochralski process is often used to make high-purity single silicon crystals for use in solid-state[?]/semiconductor devices.

In 1997, regular grade silicon (99% purity) cost about $ 0.50 per g.

Isotopes

Silicon has nine isotopes, with mass numbers[?] from 25-33. Si-28 (the most abundant isotope, at 92.23%), Si-29 (4.67%), and Si-30 (3.1%) are stable; Si-32 is a radioactive isotope produced by argon decay. Its half-life, after much argument, has been determined to be approximately 276 years, and it decays by beta emission to P-32 (which has a 14.28 year half-life) and then to S-32.

Precautions

A serious lung disease known as silicosis[?] often occurred in miners, stonecutters, and others who were engaged in work where siliceous dust was inhaled in great quantities.

Miscellaneous Information

Because Silicon is an important element in semiconductor and high-tech devices, the high-tech region of Silicon Valley, California, is named after this element.

External Links

WebElements.com - Silicon (http://www.webelements.com/webelements/elements/text/Si/index.html)
EnvironmentalChemistry.com - Silicon (http://environmentalchemistry.com/yogi/periodic/Si.html)

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